Advancements in acoustics technology mean that motor vehicles of recent design, in particular vehicles in the luxury and sports car class, are distinguished by a high level of comfort in terms of sound insulation in the passenger compartment of the vehicle. This high comfort level is here characterized by a low sound pressure level and by largely suppressed background noise. This is also true of the external noise generated by the motor vehicle, particularly in respect of the statutory regulations, according to which, in the Federal Republic of Germany, for example, a maximum sound pressure level of 74 dB(A) is permitted.
The increasingly emotive considerations attached to the use of the aforementioned vehicles and the decision to purchase them make it more important to purposely structure the internal and external noise of the motor vehicle to suit the particular type of vehicle.
Since vehicles in the luxury and sports car class have a low interior sound pressure level, it is often relatively difficult for the driver to distinguish the instantaneous load of the internal combustion engine fitted in the vehicle solely from the engine noise prevailing in the vehicle passenger compartment. This is often desirable, however, particularly in the case of sports cars, since it may be precisely these vehicles in which subjective perceptions on the part of the driver play a part in the use or in the purchase of such a vehicle.
In order to provide the driver the facility for detecting the engine load from the engine noise while underway, measures may be implemented in the sound absorption system, which can mean an increase in the external noise level. This often results in considerable noise pollution to the immediate surroundings and the wider environment. Furthermore, under statutory provisions the external noise level may be increased only to a very limited extent.
The problems described above are known, and German Published Patent Application No. 197 04 376 describes a means of acoustically connecting the filter housing of an air filter arrangement for an internal combustion engine of a motor vehicle to the passenger compartment of the motor vehicle by way of a line.
German Published Patent Application No. 42 33 252 describes a motor vehicle in which a main line from an intake or exhaust system is connected by way of a line to the passenger compartment. A diaphragm is arranged in the area where the line opens into the passenger compartment and a throttle valve adjustable as a function of an accelerator pedal is arranged between the diaphragm and the main line.
German Published Patent Application No. 44 35 296 describes a motor vehicle having an internal combustion engine, in which the intention is to improve the arrangement described in German Published Patent Application No. 42 33 252. For this purpose a pipe, which is provided with at least one acoustic resonator, adjoins the diaphragm on the side remote from the tubular section.
All of the conventional solutions operate solely with the noises generated by the internal combustion engine, which although they may be amplified and/or fed into the passenger compartment of the motor vehicle by the said measures are not susceptible to influencing or modification of the noise.
It is therefore an object of the present invention to provide a device for noise structuring in a motor vehicle, which by the simplest possible arrangement creates various, desired sound characteristics for the vehicle.